Q: Going from 2 lists of length n -> 1 list of length n, with sublists of length 2?

user_8415645 0
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To describe the problem with a small example input and desired output:

a = ['a', 'b', 'c']
b = [1, 2, 3]
c = expr

print(c)
>> [['a', 1], ['b', 2], ['c', 3]]

So I have come to a question about how to nicely perform this in a pythonic way. What I have come up with is a list comprehension that does this nicely using zip, however it does feel like a bit of a cop-out using zip in the following manner:

[[x, y] for x, y in zip(a,b)]

Is there another way?

Furthermore, since zip is not a solution for the general case with m lists of length n, that one wants to combine in the same way. Edit: As Dani Mesejo pointed out, Pythons zip built-in can take m iterables.

I'm mostly interested of nice plain python solutions. I know that numpy can do this through nice nparray concatenations :)

Thanks!

numpy-ndarray list-comprehension list numpy python
2 Answers

Direct unpacking of zip with *:

[*zip(a,b)]

Will return a list of tuples, but for if you strictly want nested 2D list, then yours is the best.

user_122698570

You can also use the chain function from itertools.

from itertools import chain

chain(zip(a,b))

Similar to the previous answer it will be a list of tuples. However, if your lists have more than 10.000.000 elements, I strongly recommend to use the chain function to achieve a better performance.

python -m timeit -n 10 "from itertools import chain;chain(zip(range(10000000),range(10000000)))"
10 loops, best of 5: 950 nsec per loop

python -m timeit -n 10 "[*zip(range(10000000),range(10000000))]"
10 loops, best of 5: 1.14 sec per loop
user_23565170
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